Cob: Re: Cob 2X wall for insulation

[John Fordice]

"Patricia L. MacKenzie" wrote:

 it sounds as if it would be possible only
> if the actual time existed to double construct.
> P.

Patricia,
Bear in mind that cob achieves its strength by being constructed as a
rather thick wall.  I believe traditional cob is something on the order
of close to 2' thick.  While there are some folks in the North American
cob movement who have experimented with walls at 8" or less thickness,
In my opinion this is getting a bit dicey in the absence of any proof
that such narrow walls will withstand an earthquake.
  
Traditional adobes that survive earthquakes run in the range of a wall
height to thickness ratio of 3:1 up to 5:1.  Beyond that there is danger
of wall failure in an earthquake.  With the inclusion of wall
stabilization via a reinforced foundation and bond beam connected
together with vertical ties in the walls, it has been tested & shown
that a wall ratio of 7:1 will survive an earthquake.

The point of the above is that until there is testing that shows us that
thin cob walls are stable in the event of an earthquake, it is prudent
to build with thick walls.

So a decision to build double cob walls just to create a void to be
filled with some form of insulation, is really creating an immense
amount of extra work.  A more optimal solution would seem to be a thick
(i.e. stable) cob exteror wall with strawbales stacked on a foundation
outside of that & covered with earth plaster.  This issue was discussed
at length on the list a while back & If I recall correctly, this as the
concensus.  It's all in the list archives.
Regards 
john fordice